The invention refers to a hoist with at least two hoisting units, with the hoisting cables or similar means of each unit extending around guide pulleys of lower or sub-pulleys to fixed points on the hoist body.
A hoist disclosed in German DE-OS No. 2 115 587 shows four hoisting units for one container with the vertical position thereof checked by a measuring device under the hoist. There are no devices preventing an overload during uneven contact with a separate support. This is of no particular disadvantage in the hoist shown in that publication, since the hoisting units engage near the four corners of the load. Thus, an uneven support cannot cause any notable overloads of one hoisting unit. Considerable overloads may occur, however, when setting down a load, if the latter was lifted by several spaced hoist units, and the load extends considerably beyond the working points of the hoist units.
It is, therefore, the object of the invention to provide a hoist with several hoisting units to transport loads, which loads may protrude far beyond the attaching points of the hoisting units in such a manner that an overload of the hoisting units is safely prevented. The device of the invention operates effectively even if the load has already made contact with an underlying support at the end opposite the hoisting unit. This is done by providing the hoisting cable of each hoisting unit with a piston cylinder arrangement, one part of which, e.g. the cylinder, may be attached to the hoist body, while the other part, namely the piston rod, may serve as the fixed or holding point or end of the hoisting cable with the hoisting unit being at the other end. The pressure chamber of the cylinder is connected to a common pressure medium system for all hoisting units via an overload check valve for exhausting the pressure chamber during excessive pressure. The extent of a possible overload is explained later in an example.
The occurrence of an overload is prevented by the overload check valve which is preferably set for a 5% overload, permitting the pressure medium to flow out of the pressure chamber of the cylinder upon the pressure reaching 5% overload, so that the fixed point of the cable yields in a sinking or lowering direction. The working distance or stroke of the piston compensates for a possible vertical elevational difference, and the displaced pressure medium flows into the pressure medium system which is equipped with an accumulator for receiving the pressure medium.
In order to prevent slack in the cable, all hoisting units are disconnected as soon as one of the overload check valves responds, and to this end each piston is equipped with a switch. Another feature of the invention provides a pressure medium pump in the pressure medium circuit for resetting so as to move the piston in a withdrawing direction, such pump feeding pressure medium into reduced-volume pressure chambers via an infeed check valve opening in the direction of the cylinder pressure chamber.
An example of the invention is shown in the drawing, which is a schematic view of the hoisting mechanism, and explained as follows.